1. Field of the Invention
This invention generally relates to signal processing and, more particularly, to an apparatus and method for phase-shifting, combining, and filtering electrical signals.
2. Description of the Related Art
FIG. 8 is a schematic diagram of a conventional lumped element, dual input-single output system in a wireless communications device. A wireless communications device will be used to illustrate the phase-shifting, combining, and filtering of communications signals. However, it is understood that the following discussion is applicable to a wide variety of electronic devices and signals. In a wireless communications device, a lumped element circuit, as shown in FIG. 8, can be used to phase-shift input signal A and to combine and filter phase-shifted signal A and input signal B to produce an output signal. In FIG. 8, lumped element transformers and energy-storage devices, such as capacitors, are used to process the input signals. In one instance, for a Code Division Multiple Access (CDMA) wireless device, the transformers are driven in and out of saturation to produce a CDMA waveform at the system output.
Unfortunately, there are disadvantages associated with the lumped element system in FIG. 8. The lumped element system is only effective for signal frequencies up to approximately 200 MHz. Beyond this frequency, the system becomes excessively lossy. In general, lumped elements also are larger and more expensive than other types of elements, for example, distributed elements. Advances in technology and manufacturing techniques permit wireless communications devices to be made increasingly smaller, which in turn, creates a need to reduce the space required for components in the devices by reducing the number and/or size of the components. Unfortunately, as noted above, lumped elements tend to be relatively larger. The subsequent increase in space usage can limit the size to which a wireless device can be reduced, or can limit space available in the wireless device for other components.
It would be advantageous if a system could efficiently phase-shift, combine, and filter signals at frequencies greater than 200 MHz.
It would be advantageous to reduce the size and cost of a system to phase-shift, combine, and filter signals.